In these years, as the environmental regulations are tightened worldwide, automakers are each actively promoting developments in terms of lower emission and lower fuel consumption. Therefore, the conventional mechanical engine control mechanism is being replaced with an electronic engine control mechanism. Accordingly, it is required that a magnetic material which is a core part of the control mechanism has higher performance and a smaller size. In particular, developments are being promoted of a material having high magnetic properties in medium and high frequency ranges in order to achieve more precise control with smaller power. For a material to have high magnetic properties in medium and high frequency ranges, the material has to have all of high saturation flux density, high magnetic permeability and high electrical resistivity. While a metal magnetic material generally has high saturation flux density and high magnetic permeability, the metal magnetic material has a low electrical resistivity (10−6 to 10−4 Ωcm) and thus has a large eddy current loss in middle and high frequency ranges. Therefore, the metal magnetic material has its magnetic properties deteriorated and thus is difficult to use singly. A metal oxide magnetic material has a higher electrical resistivity (1 to 108 Ωcm) as compared with the metal magnetic material, and thus has a smaller eddy current loss in middle and high frequency ranges and less deterioration of its magnetic properties. However, since the saturation flux density of the metal oxide magnetic material is one-third to half that of the metal magnetic material, the use of the metal oxide magnetic material is limited. In view of these conditions, a composite magnetic material has been proposed that is a composite of a metal magnetic material and a metal oxide magnetic material and thus has high saturation flux density, high magnetic permeability and high electrical resistivity to compensate for respective defects of the metal magnetic material and the metal oxide magnetic material.
A composite magnetic material as described above is disclosed for example in Japanese National Patent Publication No. 10-503807 (Patent Document 1) that discloses a method of forming the composite magnetic material by joining, by means of an organic material such as polyphenyleneether, polyetherimide, amide oligomer, a plurality of composite magnetic particles that are each an iron particle with its surface covered with an iron phosphate film.    Patent Document 1: Japanese National Patent Publication No. 10-503807